[BE][CI] remove flakiness calculation in print_test_stats.py (#79905)
We now use Rockset to store test case stats and we can glean flakiness from that data, so this complicated logic isn't necessary anymore!
This will also prevent spurious red on trunk that occurs with this code e.g., https://github.com/pytorch/pytorch/runs/6968080598?check_suite_focus=true
## test plan
print_test_stats work on the PR: https://github.com/pytorch/pytorch/runs/6974961237?check_suite_focus=true though it seems several jobs ran into HTTP 500 and Memory errors which I don't think is related to my code + more a problem with the server https://github.com/pytorch/pytorch/runs/6974938954?check_suite_focus=true
Pull Request resolved: https://github.com/pytorch/pytorch/pull/79905
Approved by: https://github.com/zengk95, https://github.com/seemethere
